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Study on Entanglement and Squeezing in a Cavity EIT System

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Tutor: HouBangPin
School: Sichuan Normal University
Course: Theoretical Physics
Keywords: Cavity QED,Electromagnetically induced transparency,CavityInput-output theory,En
CLC: O431.2
Type: Master's thesis
Year:  2013
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Electromagnetically Induced Transparency (EIT) is one of the special physical phenomenon due to the interference phenomenon between light and atomic system. In general, light can be absorbed by the atomic system and the dispersion is great when the probe light interacts with medium. But the atomic medium is the transparent for the probe light, when the atomic system is driven by a strong coupling light. Since Harris observed the EIT phenomenon by utilizing pulsed laser interacting with three-level Sr atom in1991, it has attract much attention because of its applications in quantum computation, quantum information, and storage of optical information. The EIT in atomic system has been generalized to cavity system. At the same time, the single-photon EIT has been generalized to two-photon or multi-photon ones. The EIT with a single transparency window has been generalized to two or multi-ply EIT. This plays an important role in multi-channel optical communication and quantum communication. On the other hand, the quantum properties (such as entanglement and squeezing) of light will be changed, when the light is via the electromagnetically induced transparency medium. This is useful in obtaining ideal entanglement and squeezing, which is a potential application in quantum computation and quantum communication. We organize this thesis as follows:In chapter1, we have reviewed the EIT phenomenon, its development as well as the various applications and present studies on the EIT.In chapter2, the interaction between the cavity and the atoms by using full quantum theory has been presented, and the Jaynes-Cummings model and cavity input-output theory are also introduced. At the same time, we choose a two-level atomic system as an example to demonstrate these physical phenomena.In chapter3, the basic theory of entanglement and squeezing, which contains their definitions, classifications and the criterions of entanglement and squeezing, is introduced.In chapter4, the single and two-photon electromagnetically induced transparency can be modulated by using a coherent field to drive the transition connected by the ground level of the coupling transition in an inverted-Y scheme atomic system and another level. The coherent field influences the single and two-photon absorption properties in the similar way. There appears one absorption peak induced by the coherent field and this peak splits the single transparency window into two parts. The height of the peak and the frequency width of the transparency spectra are closely dependent on the strength of the coherent field. These phenomena are explained by using the dressed-state. This can be useful in multi-channel optical communication and controllable manipulation of the atomic optical properties.In chapter5, The output squeezed spectrum and entanglement of the output two modes from a cavity QED system which is embedded by a four-level atom driven by two classical fields are investigated. The influence of the cavity decay rates, relative phase between two classical fields, and effective coupling constants between the atom and the cavity on the entanglement and squeezing are studied. It is shown that the depth of the squeezing spectrum is insensitive to the cavity decay rates but sensitive to relative phase and effective coupling constants. On the other hand, the width of the squeezing spectrum is dependent on the cavity decay rates and the coupling constant. The perfect EPR-like entanglement can be obtained by adjusting the suitable parameters. This will be extremely useful in quantum communication and computation.
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